Interesting thread. I also have a meniscal tear and it is good to hear of other experiences. Mine doesn't really affect my running (I have done two marathons on it) just things requiring deep flexion such as kneeling and squatting and it also hurts at night sometimes.
The surgeon I saw recently after an MRI said that I could opt for an arthroscopy but that if it was his knee, he would leave it. At the moment I am still thinking about it... He also told me that the op would mean at least 8 weeks before I could start running again. As I am just coming back after injury (unrelated) that would be really frustrating and is one thing that is putting me off!
His opinion was that physio would not be of any use in trying to increase range of movement.
I think it's purely down to whether you're a lark or an owl, not hydration or nutrition. I much prefer to race in the evenings, providing of course that I haven't had a really tiring or stressful day. I did also read somewhere that research shows most athletes race better in the evening.